Liquid-crystal panels in Twisted Nematic (TN) mode, Vertical Alignment (VA) mode or In-Plane Switching (IPS) mode are used for liquid-crystal display device. When using a liquid-crystal display panel in TN mode, a polarlizer laminated to each of opposite surfaces of the liquid-crystal display panel is configured with a polarizing film sheet cut in an angle of 45° with respect to a stretching direction. Stretching directions of the polarlizers on each of the opposite surfaces of the liquid-crystal display panel are arranged as orthogonal to each other, i.e., in a crossed-Nicol arrangement. To this, optical film laminate sheets configured as that polarizing film sheets punched out into rectangular-shaped sheets which long sides or short sides thereof being oriented to 45° or 135° with respect to the stretching direction and superimposed with other film components are normally used.
On the other hand, in configurations where a liquid-crystal display panel in VA mode or IPS mode is used, a polarizing film sheet is formed by cutting in a direction orthogonal or parallel with respect to the stretching direction. Polarizing film sheets formed as such are laminated on each of the opposite surfaces of the liquid-crystal display panel so that an absorption axis of the polarizing film sheets on one side is orthogonal to that of the polarizing film sheets on the other side, i.e., in a crossed-Nicol arrangement. Thus, in configurations where a liquid-crystal display panel in VA mode or IPS mode is used, a long web of optical film laminate comprising a long web of polarizing film is cut to a size of the liquid-crystal display panel on a long web of carrier film to allow for forming a plurality of optical film laminate sheets on the carrier film, conveying the plurality of optical film laminate sheets to a lamination station for laminating with a plurality of liquid-crystal display panels in a state supported on the long web of the carrier film, releasing the plurality of optical film laminate sheets from the carrier film at the lamination station and sequentially laminate the plurality of optical film laminate sheets on each of the opposite surfaces of the liquid-crystal display panels. The plurality of optical film laminate sheets comprises so-called absorptive polarizing film sheets.
In a manufacturing system of liquid-crystal display device, a plurality of optical film laminate sheets to be sequentially laminated with a plurality of liquid-crystal display panels are conveyed to a lamination station in a state being supported on a long web of releasing film or a carrier film, peeled from the carrier film at the lamination station and continuously laminated with the liquid-crystal display panels. Since manufacturing system of liquid-crystal display device is a continuous lamination unit, it is referred in the following description as “a continuous lamination” system or “a roll-to-panel” (“RTP”) system, in order to differentiate from an individual lamination system in which a plurality of optical film laminate sheets formed in a size of a liquid-crystal display panel is prepared, and each of the plurality of optical film laminate sheets is laminated one by one to each of the liquid-crystal display panels.
Specifications of Japanese Patent 4307510B (Patent Document 1), Japanese Patent 4451924B (Patent Document 2) and Japanese Patent 4669070B (Patent Document 3) disclose method and apparatus for manufacturing liquid-crystal display panels in which polarizing film sheets are laminated on each of opposite surfaces of the liquid-crystal display panels such that a transmission axis of the polarizing film sheets on one side is perpendicular to that of the polarizing film sheets on the other side. The manufacturing system shown as an example in FIG. 1 and FIG. 2 of the Patent Documents has a first lamination station and a second lamination station arranged apart in a longitudinal direction on a straight channel, and a feed line for feeding a long web of a first or a second optical film laminate comprising polarizing film toward the channel is provided at each of ends of the straight channel. In the first lamination station, a panel component carry-in line for conveying rectangular panel components from a direction orthogonal to the channel and a carry-out line for conveying the rectangular panel components laminated with the optical film laminate sheets comprising polarizing films to a direction orthogonal to the channel from the second lamination station are provided. Between the first and the second lamination stations, there is provided a means for rotating panel components respectively laminated with a first optical film laminate sheet on one side thereof in a state supported on a carrier film within a plane including the panel components.
Japanese Laid-Open Patent Publication JP2009-122641A (Patent Document 4) and Japanese Laid-Open Patent Publication JP2005-037417A (Patent Document 5) also discloses method and apparatus for manufacturing liquid-crystal display device in which polarizing film sheets are laminated on each of opposite surfaces of the liquid-crystal display panels such that a transmission axis of the polarizing film sheets on one side is perpencidular to that of the polarizing film sheets on the other side. For example, systems shown in FIG. 7 of Patent Document 4 or in FIG. 6 and FIG. 7 of Patent Document 5 comprise two channels orthogonal to each other. Rectangular liquid-crystal display panels are continuously conveyed with their long sides at front in a first channel of the two channels. In the first channel, optical film laminate sheets, formed by cutting a long web of optical film laminate with a configuration of other optical film laminated on a polarizing film into a size corresponding to a liquid-crystal display panel, are laminated on one side of liquid-crystal display panels conveyed along the channel. The liquid-crystal display panel, to which the optical film laminate sheet is laminated on one of the opposite surfaces thereof, is reversed upside down and then transferred to a second channel which is orthogonal to the first channel. In the second channel, the liquid-crystal display panels are continuously conveyed with their short sides at front, and optical film laminate sheets with a similar configuration as the above described optical film laminate sheets are laminated on the other side of the liquid-crystal display panels.
Any of the lamination units disclosed in the above described Patent Documents is configured to sequentially laminate one of two polarizing film sheets to each of opposite surfaces of a liquid-crystal display panel in two laminating steps such that a transmission axis of one of the two polarizing film sheets is orthogonal to that of the other.
On the other hand, Japanese Laid-Open Patent Publication JP2009-271516A (Patent Document 6) discloses a lamination unit for laminating an optical component to an optical display unit in three laminating steps. When referring to FIG. 3 of Patent Document 6, there is disclosed a lamination unit for sequentially laminating a first, a second and a third optical component to an optical display unit which may be configured as a liquid-crystal display panel. The first, the second and the third optical component are a polarizer and a pair of polarizer protection film for protecting the polarizer on the opposite surfaces of the optical display unit.
Patent Document 6 discloses a combination of a first, a second and a third optical component different from the above. Each of the first, the second and the third optical component is manufactured as a web of laminate having an optical component, an adhesive layer laminated on the optical component and a releasing film, and the web of laminate is prepared as a material wound in a roll shape. A conveying channel for conveying an optical display unit to one direction is provided in the lamination unit and a feed line for the first, the second and the third optical component is provided above the conveying channel, the releasing film is peeled from the web of laminate fed from the feed line, and each of the optical components is sequentially laminated to the optical display unit in three step process. The first, the second and the third optical component laminated in the three step process configure an optical film laminate which achieves desired optical performance when those optical components are laminated thereon.
In recent years, smartphones and tablet terminals are universally distributed as high-performance portable terminals with built-in battery. Those portable terminals are referred as slate-PCs, and in many cases, a middle-sized or small-sized liquid-crystal display device is used as an optical display device. A liquid-crystal display device to which a reflective polarizing film is used has been developed. This is because attention has been drawing to a benefit that a reflective polarizing film is able to enhance brightness of a display screen by switching reflected or absorbed light to transmitted light and is advantageous for efficient use of power charged in a battery. A Liquid-crystal display panel used for a middle-sized or small-sized liquid-crystal display device in general is configured to contain a liquid-crystal (LC) cell with a size of about 5 to 10 inches (120 to 250 mm), and a color filter (CF) is arranged on a viewing side of a LC cell and a thin-film transistor (TFT) is arranged on a non-viewing side thereof, thickness of a LC cell is about 0.5 mm and weight thereof is about 15 to 40 grams. On the contrary, a LC cell for a television has a size of 18 inches (450 mm) even for a small one, and the size exceeds 60 inches (1500 mm) for a large one. Thickness of such LC is 1.4 mm which is 3 times or more than that of a LC cell for a slate-PC, and weight is 300 to 3,500 grams.
Requirements for processing capacity of a manufacturing system of the middle-sized or small-sized liquid-crystal display device used for a slate-PC are different from those of a manufacturing system of liquid-crystal display device for a television. Difference in requirements may include accuracy and speed of laminating an optical film laminate sheet comprising a polarizing film to both of opposite surfaces of a liquid-crystal display panel, and ease of process for weight reduction. In addition, requirements to minimize contamination in a clean room are different from those a manufacturing system of liquid-crystal display device for a television as that it is necessary to minimize dead space and to maintain appropriate level of a processing table to facilitate processing table of a long web of optical film laminate in use. Further, when a reflective polarizing film is used, it is required to continuously perform a process of laminating a reflective polarizing film sheet on a surface of an absorptive polarizing film sheet laminated on a non-viewing side of a liquid-crystal display panel such that a transmission axis of the absorptive polarizing film sheet is parallel to that of the reflective polarizing film sheet.
A reflective polarizing film is also referred as a brightness-enhanced film. Structure and function of the reflective polarizing film are different from those of an absorptive polarizing film which is a general polarizing film. Specification of U.S. Pat. No. 6,113,811 (Patent Document 7) and PCT Japanese Publication JPH9-507308A (Patent Document 8) disclose manufacturing and function of a reflective polarizing film. As an aid to understand techniques of the present invention, manufacturing and function of a reflective polarizing film is outlined in the following.
A reflective polarizing film is manufactured by steps of: isothermally and simultaneously squeezing high-birefringent material which develops strong birefringence upon stretching and zero-birefringent material which scarcely develops birefringence upon stretching as a plurality of layers mutually overlapping; and stretching squeezed multi-layered materials to 3 to 5 times to a transverse direction orthogonal to a squeezing direction. Typically, a multi-layered material consisting of 100 or more alternating layers is formed and stretched to a thickness which causes optical interference between adjacent layers to make a thin long web of optical film. In such configured reflective polarizing film, a longitudinal direction i.e. a squeezing direction thereof is a transmission axis and a transverse direction i.e. a stretching direction thereof is a reflection axis. That is, orientation of a transmission axis of the above reflective polarizing film is opposite with respect to stretching direction to that of an absorptive polarizing film having an absorption axis corresponding to a reflection axis in longitudinal direction and a transmission axis in transverse direction.
Functions of a reflective polarizing film is described as follows. In light incident to a reflective polarizing film, component of the light along a transmission axis corresponding to about 50% of incident light transmits through the film and component of the light corresponding to the remaining 50% is reflected at an interface of alternatively arranged adjacent layers with different refraction index. The reflected light is again reflected at a next interface and component of light corresponding to about 25% of the reflected light transmits along the transmission axis. As such, in a configuration using a reflective polarizing film, as a result of repetition of transmission and reflection, utilization factor of light used is not 50% but close to 100% of light transmitting the reflective polarizing film. Although the reflective polarizing film is very expensive, it is recently heavily used because of significant enhancement of brightness.
As described in the above, a reflective polarizing film is totally different in structure and function from an absorptive polarizing film generally formed with a single layer of PVA film. In case where a reflective polarizing film is combined with an absorptive polarizing film for use in a liquid-crystal display device, there may be certain restrictions accompanied with manufacturing steps including lamination of the films to a liquid-crystal display panel because structure and function of the reflective polarizing film are different from those of the absorptive polarizing film. For example, when an absorptive polarizing film is combined with another absorptive polarizing film, there is no problem in sequentially laminating an absorptive polarizing film in a continuous step to each of opposite surfaces of a liquid-crystal display panel because a relationship between a stretching direction and an absorption axis or a transmission axis is identical between the two absorptive polarizing films, as shown in Patent Documents 1 to 5. But, when attempting to laminate an absorptive polarizing film to a reflective polarizing film such that transmission axes of those films match, it is difficult to continuously laminate because transmission axes of those films are inverse with respect to a stretching direction.
Thus, in case where a reflective polarizing film is laminated to an absorptive polarizing film to manufacture a long web of two-layered laminate, two long webs of optical film laminate comprising an absorptive polarizing film and a reflective polarizing film respectively are fed from respective rolls, and each of the optical film laminate is overlapped in direction orthogonal to each other to form a two-layered laminate laminated with an adhesive agent, and the two-layered laminate is cut to form a rectangular mother sheet.
Japanese Laid-Open Patent Publication JP2010-032900A (Patent Document 9) or Japanese Laid-Open Patent Publication JPH11-231129A (Patent Document 10) disclose a method for manufacturing a mother sheet consisting of rectangular multi-layered optical film laminate, and a method for manufacturing a plurality of optical film laminate sheets by punching out or cutting the mother sheet to a size of a liquid-crystal display panel. Use of the methods disclosed in the Patent Documents allows for preparing in advance many two-layered optical film laminate sheets in which a reflective polarizing film and an absorptive polarizing film sheet are overlapped for manufacturing steps where the two-layered optical film laminate sheets are laminated to liquid-crystal display panels. In this case, it is essential to prepare many two-layered optical film laminate sheets in advance for a lamination apparatus for manufacturing a liquid-crystal display device.
The prior art documents referred to in the above and the following descriptions are listed below.    Patent Document 1: Japanese Patent No. 4,307,510B    Patent Document 2: Japanese Patent No. 4,451,924B    Patent Document 3: Japanese Patent No. 4,669,070B    Patent Document 4: Japanese Laid-Open Patent Publication 2009-122641    Patent Document 5: Japanese Laid-Open Patent Publication 2005-037417A    Patent Document 6: Japanese Laid-Open Patent Publication 2009-271516A    Patent Document 7: U.S. Pat. No. 6,113,811    Patent Document 8: PCT Japanese Publication H9-507308A    Patent Document 9: Japanese Laid-Open Patent Publication 2010-032900A    Patent Document 10: Japanese Laid-Open Patent Publication H11-231129A    Patent Document 11: Japanese Patent No. 4,551,477B    Patent Document 12: Japanese Patent No. 4,377,961B    Patent Document 13: Japanese Patent No. 4,361,103B    Patent Document 14: Japanese Patent No. 4,377,965B